This invention relates to a planar semiconductor device.
Heretofore, it has been known that a binary compound semiconductor such as GaAs exhibits an electron transfer effect under an electric field due to its multi-valley band structure and produces a high electric field domain therein with the result that current pulses or current oscillation will be generated. This semiconductor is therefore utilized as a Gunn diode and a micro-wave oscillator. Furthermore, GaAs has a wide forbidden gap and can itself be used an insulating material. Thus an active layer of GaAs of n-type is epitaxially grown on the insulating material as a substrate and electrodes are applied to the active layer in the planar form, thus enabling use of the formed element as a planar device (Transferred Electron Devices by P. J. Bulman et al 1972, Academic Press). Particularly, an element having a Schottky electrode at the center thereof as well as electrodes for bias application provided at opposite ends thereof has been developed as an ultra-high speed digital element in an integrated form. (GALLIUM ARSENIDE and RELATED COMPOUNDS (ST LOUIS) 1976, Inst. Phys. Conf. Ser. No. 33b, 1977, p245-253).
However, GaAs has certain drawbacks. For example, an electric field of as high as about 3 KV/cm is required to produce the above effect and therefore power consumption becomes high and high density integration becomes difficult. In order to eliminate these drawbacks, a ternary compound semiconductor of Ga.sub.y IN.sub.1-y Sb was proposed. Measurement of the electrical performance of this semiconductor conducted by the inventors revealed that the threshold electric field at which a high electric field domain is produced is about 600 V/cm, which is one fifth of that for GaAs, and that power consumption is reduced to about one-thirtieth (GALLIUM ARSENIDE and RELATED COMPOUNDS (EDINBURGH) 1976, Inst. Phys. Conf. Ser. No. 33a, 1977, p296-305). Use is made of InSb or GaSb which have closely matching lattice constants to provide epitaxial growth on the above-mentioned semiconductor. However, neither of these two materials presents insulating characteristics at room temperature and thus cannot be used to form electrically separate elements in an integrated form to provide a planar structure as is possible in the case of GaAs. It was therefore impossible to manufacture a digital element with a gate electrode. Nevertheless, semiconductors of III-V compound having a narrow energy gap (For example, InSb, InAs, GaSb and such combinations thereof as Ga.sub.y In.sub.1-y Sb, GA.sub.y In.sub.1-y Sb.sub.y As.sub.1-y and InAs.sub.y Sb.sub.1- y) have promising characteristics in connection with a number of possible applications such as:
(i) low-voltage mircowave oscillators or low-power consumption high-speed logic elements, in view of the fact that they present a Gunn effect at a low electric field. PA1 (ii) galvano-magnetic elements, in view of the large galvano-magnetic effect that results from their high mobility. PA1 (iii) elements for emitting and detecting infrared rays in view of the fact that they have a band gap in the infrared region of wavelength 1.0 to 5.0 .mu.m.
However, because of the big difference in lattice constant high quality crystals cannot be obtained by growth on semiconductors having a large energy gap such as InP and GaAs. Use of semiconductors having similar narrow energy gaps as the substrate is not successful because their low resistances do not allow electrical separation of elements. Integration is thereof difficult.
It is therefore an object of the present invention to provide a planar semiconductor device having a narrow energy band gap semiconductor as the active layer.
Another object of the present invention is to provide an integrated planar semiconductor device having a narrow energy band gap semiconductor as the active layer.